Two studies have been initiated to study the role of NS1 in the dengue virus life cycle. The first is the introduction of mutations into the full length dengue 2 clone. In vitro transcribed RNA from mutant and full length cDNA clones is transfected into susceptible LLC-MK2 cells. At times post-transfection, virus replication is assayed by analyzing viral antigen production and viral RNA replication. A mutant which contains a forty amino acid deletion in the NS1 open reading frame will not replicate in LLC-MK2 cells. The second study is the establishment of LLC-MK2 cells expressing NS1. These cells express low levels of dengue 2 NS1. Cells expressing NS1 are able to complement NS1 mutant dengue 2 genomes. These cells will be used to make stocks of mutant virus, and to study the processing and secretion pathways of NS1.